Deluxe Memory Man Grounding Problems

[Primus]

I'm having terrible noise and grounding problems with my reissue Deluxe Memory Man. When the pedal is in true bypass mode and not plugged into power, there is no noise. If you plug it into power, there is some hum. Then if you stomp the switch there is a lot more hum. The configuratio I am using is guitar-->memory man--> amp and the amp and memory man share a common ground.

I was advised to start out by first using plastic washers to isolate all of the jacks. I tried this out, but I still have all the hum and now the stomp switch pops.

The grounding scheme goes like this:

From 120V AC power cord, the hot and neutral go to the primary side of the transformer. The safety ground goes to the lug of the transformer and the case. The primary C.T. is unused in heat shrink. On the secondary side, the two secondary wires go to the board and the C.T. goes to the ground pad on the board. This is a bipolar power supply, I think. Coming off of the ground pad is another wire that goes to the ring of the "echo out" mono output jack. A small ceramic cap is soldered across to the tip of the echo out jack. Unshielded bus wire connects the rings of "echo out", "direcet out" and "input" in series. Finally, there is one wire that comes off the grounding pad that goes to the 3PDT to ground the effect signal when bypassed. That's all she wrote for the grounding, I think. How can I squash this noise?

[Primus]

Bump.

The grounding pad on the PCB is fairly large so I'm going to go ahead and start by star grounding the three jacks and drilling new holes in the pad. Does anyone have any comments on to insulate or not to insulate the jacks from the case?

[Processaurus]

I think I remember this coming up before, its a ground loop, plain and simple.  Did you try using a ground lift yet?  If the problem goes away, you figured it out.  You can use a ground lift on the memory man all the time, which could potentially lead to electrocution if the mains were to come loose somehow inside the box and the amp wasn't plugged in and you had your hand on guitar strings and the other on something grounded.  To be ultra safe (and this is what EH shoulda done), one could insulate all the jacks from the chassis, connect the chassis to the third prong on the power cord, and connect the jacks ground (guitar and amp ground) together with the circuit ground (the center tap of the secondary, and the pad you were talking about).  That way everything except the chassis is going to ground at the amp, and the chassis is going to ground through its plug.  Make sense?  Star grounding won't be neccessary or even helpful for your problem, because there are still 2 paths to ground (through the amp and through the MM ac plug) because the circuit ground is connected to chassis ground via the echo out sleeve solder lug, and the chassis is connected to the 3rd prong, sounds like.  When you have the two grounds seperated, you should beep them out to check they aren't connected.

[Primus]

I do remember visiting this before, but I have been unable to obtain decent results on my own. I completely agree that it is a ground loop, I am just having trouble hunting it down. I tried to lift the ground again this morning, but the noise got much much worse.

So to recap:

Stock: Noisy. Ground lift does not help.

Insulated input and output jacks w/ plastic washers: Noisy, but now the switch pops. Ground lift makes buzzing worse (!?)

Next steps: Wire each individual jack to the ground pad on the board instead of in a daisy chain. There is also a switch for chorus or vibrato on the case. I'm wondering if I need to ferret out a ground connection here too.

[Processaurus]

hmm, I wonder if its not the grounding on the pedal, but the input getting the hum as cross talk from the AC being in there.  Heres an experiment, do you have a buffered pedal (boss for example) you can put in front of it? if you do, see if the dmm still hums the same when in bypass.  If its an issue of crosstalk, the lower impedance of the buffered pedal should reduce it.

[Primus]

I have run the DMM last in a chain of several buffered pedals. I will try it simply today going guitar-->BOSS tuner-->DMM-->amp. I'll try to confirm that the signal ground and earth ground are in fact seperated.

NiftyDog comments in this thread about interference in another EHX pedal. He was thinking it was DC in the output jack: http://www.diystompboxes.com/smfforum/index.php?topic=29486.0

[aron]

I had problems like this as well. I lifted the grounding pin on the memory man for certain situations. hmmmmm

[Primus]

I know! It's driving me batty because the ground lift actually makes it much worse.

[Primus]

Well, I tried a tube screamer before and after the pedal with no effect on the noise the pedal generates even when in bypass. This one isn't getting solved w/o a meter.

[aron]

The ground lift makes it worse? Wow, I wonder what's going on?